Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With readOnlyHint=true already covering the safety profile, the description adds genuinely useful context: it enumerates the returned fields (name, company, emails, phone numbers) plus custom fields, and maps to the REST endpoint GET /contacts. It omits pagination behavior and rate limits, but the added return-shape detail is meaningful, especially with no output schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, zero filler, front-loaded with the core action and scope; filters and return content follow in priority order.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a read-only list tool with no output schema, the description covers return content and the endpoint, which is what an agent needs to interpret results. Pagination is documented in the schema via pageToken/nextPageToken, so the only minor gap is not stating paging behavior in prose.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents all four parameters including filter semantics and the pageToken/maxResults constraints. The description only restates that externalIds and sources act as filters, adding no syntax or format detail beyond the schema; baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource with scope ('List contacts in the workspace') and names the two filter dimensions. It doesn't explicitly contrast with the singular openphone_get_contact sibling, so an agent must infer list-vs-get from the name.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'optionally filtered by external ids or sources' implies when the filters are useful, but there is no explicit when-to-use guidance, no prerequisites, and no named alternative (e.g., get_contact for a single record). Usage is implied rather than stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.